Modem computer systems require large quantities of information storage. To meet this requirement computer data storage is available in many forms. A fast, but expensive, form of data storage is main memory, typically including monolithic semiconductor circuits. Other available forms of data storage include magnetic direct access storage devices, magnetic tape storage devices, and optical recording devices. These types of data storage actually store data on electromagnetic or optical media. Each of these other types of data storage has a greater storage density and lower cost than main memory. However, these other devices require mechanical movement and therefore have slower data access times than purely electronic main memory.
Storing all system data in main memory is costly; however, storing all system data on one or more peripheral storage devices reduces performance. Thus, a typical computer system includes both main memory and one or more data storage devices arranged in a data storage hierarchy. In such a hierarchy, main memory is often referred to as the primary data storage. The next level of the hierarchy is known as the secondary data storage, and so on. Generally, the highest level of the hierarchy has the lowest storage density capability and capacity and highest cost. Down through the hierarchy, storage density and capacity generally increases and associated costs generally decrease. By transferring data between different levels of the hierarchy, as required, cost and performance are optimized.
In order to have the information available on an “as needed” basis, much storage at the lowest level of the hierarchy is required. Business applications typically use numerous portable data storage media including floppy disks, optical disks, or magnetic tapes, to meet the required data storage needs. Prior art data storage libraries have been developed to manage the storage of such portable disks or tapes. Some storage libraries employ automatic means including robotic picker and gripper devices to store and access such portable data storage media. Others do not employ automatic means, but rather rely on human operators to store and access conventional portable data storage media when needed. Those storage libraries relying on human operators are referred to as “manual data storage libraries”.
Manual data storage libraries remain popular as a choice over automated libraries because manual libraries do not require as large a capital investment. Also, manual libraries allow a human operator to maintain more control over the library. Prior art manual data storage libraries include a plurality of storage bins or slots for retaining portable data storage media, such as magnetic tapes, magnetic disks, or optical disks. Each portable data storage medium may be contained in a cassette or cartridge housing for protection. An operator must be alerted to transfer a certain portable data storage medium from a storage slots to one of only a few available disk drive units. In this regard, a disk drive unit having a portable data storage medium mounted therein and allocated for use is referred to as “unavailable”. Conversely, a disk drive unit without a portable data storage medium mounted therein, or unallocated, is referred to as “available”. Once a portable data storage medium is mounted in a drive unit, and the medium is allocated for use, data may be written to or read from that medium for as long as the system requires. Data is stored on a medium in the form of one or more files, each file being a logical data set.
What is required is a cost-efficient manual data storage library which is capable of storing more data therein than can prior art systems. Applicants' invention fulfills this requirement. Applicants' invention includes a data storage and retrieval system comprising a plurality of hard disk drive units removable disposed within a plurality of hard disk drive storage slots. Applicants' invention further includes a method to add additional hard disk drive units to Applicants' hard disk drive library, and a method to store and retrieve data stored on the hard disk drive units removable disposed with Applicants' library.